Objects that are being manufactured using processes involving application of liquids and other fluids often require that the parts be thoroughly dried before the manufacturing process can continue. For example, in fabrication of integrated circuits, doping, photomasking, etching and passivation processes often require application of particular liquids at one stage and removal of liquid residues before the next stage proceeds. Drying and removal of these liquid residues must be complete, but the drying process should, ideally, occur in a relatively short time interval and with expenditure of a minimum of energy and chemicals to implement the drying process.
Several workers have disclosed methods for drying parts, including integrated circuits, by use of heated or superheated gases. McConnell et al, in U.S. Pat. No. 4,577,650, No. 4,633,983, No. 4,738,272, No. 4,778,532, No. 4,856,844, No. 4,899,767, No. 4,911,761, No. 4,917,123 and No. 4,984,597, disclose methods of drying semiconductor wafers by flowing a heated vapor or fluid past the wafers to be dried in a vessel, as part of a wafer processing sequence. The preferred drying vapor is superheated isopropanol, which forms a minimum boiling azeotrope with water and is believed to displace water from the wafer surfaces, and the vapor flows into the vessel at one end and simultaneously flows out of the vessel at another end.
In U.S. Pat. No. 5,383,484, Thomas et al disclose use of a plurality of megasonic beam transducers, located at staggered positions, for cleaning wafers. Each transducer emits a vibratory megasonic beam with an unspecified (very high) frequency in a fixed direction, and the transducer locations are chosen so that the collection of beams irradiate, and thereby clean, all wafer surfaces in a chamber, no matter how the wafers are arranged.
Use of ultrasonic transducers in a chemical cleaning bath to cooperatively remove contaminants and unwanted material layers from semiconductor wafers, medical instruments and other objects of interest is disclosed by Erickson et al in U.S. Pat. No. 5,178,173, by Watanabe et al in U.S. Pat. No. 5,203,798, by Tamaki et al in U.S. Pat. No. 5,227,001, by Evans et al in U.S. Pat. No. 5,248,456, by Smith et al in U.S. Pat. No. 5,337,446, by Koretsky et al in U.S. Pat. No. 5,368,054, by Steinhauser et al in U.S. Pat. No. 5,380,369, by Shibano in U.S. Pat. No. 5,447,171, by Awad in U.S. Pat. No. 5,464,477, by Kato in U.S. Pat. No. 5,467,791, by Thjietje in U.S. Pat. No. 5,468,302 and by Campbell in U.S. Pat. No. 5,472,005.
Use of ultrasonic transducers to coat, spray, deposit or otherwise apply a desired material to an object surface is disclosed by Bachmann in U.S. Pat. No. 5,387,444, by Erickson et al in U.S. Pat. No. 5,409,163, and by Versteeg et al in U.S. Pat. No. 5,451,260. An ultrasonic fogging device is disclosed by Munk in U.S. Pat. No. 5,454,518.
These approaches heated or superheated gases or direct beam irradiation to dry an object surface; or they use cooperative action by an ultrasonic beam and an active chemical bath to remove contaminants from, or to apply a desired material to, an object surface. These approaches are complex, usually require operation at high temperatures, often require processing times of several minutes, and often require use of specially resistant chamber walls for the processing chamber.
What is needed is a method and associated apparatus for drying and cleaning objects in a manufacturing process that works well at room temperature and is simple, that is demonstrably complete, with no significant residues, that can be accomplished in times as short as one minute, that can be performed in a chamber with chamber walls made of almost any material, and that requires use of only a very small amount of a drying agent, with minimal expenditure of energy, particularly thermal energy. Preferably, the process should be performable over a wide range of temperatures, and should be easily scalable to any size surface.